The overall objective of this project is to understand the antibody response, and the approach is to use the tools and methods of classical and molecular genetics to reveal its components, mechanisms and regulation. The focus of this program is the immunoglobin heavy chain locus, lgh. The proposed studies will continue the examination of the structure and expression of heavy chain variable region (Vh) genes in laboratory mice and the evolution of the function, structure and contents of the lgh locus in mice, rodents and other mammals. A newly identified sequence element present in certain Vh genes has been strongly conserved during mammalian evolution. This element will be further characterized and its function and the reason for its conservation will be identified. The neighboring regions of mouse chromosome 12 will be studied to learn more about the history and function of lgh. These studies will include refinement of the genetic and physical maps of the mouse lgh locus, the identification of new RFLP markers in and around lgh by subtractive cloning from allotype congenic strains, genetic dissection of the control of dominant or recurrent idiotype expression, measurement of Vh gene family expression by reverse Northern blotting, investigation of the genetic control of the expressed repertoire, cloning and sequencing Vh genes from diverse mammalian species, analysis of the physical location and developmental expression of highly conserved Vh genes in other mammals, cloning and sequencing duplicated and deleted Vh genes from mice, and evolutionary studies on polymorphism and heterozygosity of lgh in various species. In addition, the Tsu locus will be cloned and the function of these T cell proteins in the regulation of the antibody response determined.